Radio apparatus



P 1934- J. M. MILLER Er AL 1,973,293

RADIO APPARATUS Original Filed Oct. 23. 1928 2 ets sheet l Sept. 11, MILLER AL RADIO APPARATUS Original Filed Oct. 23, 1928 2 Sheets-Sheet 2 Patented Sept. 11, 1934 rrss if i PET Bryn Mawr, Pa, assigncrsto Atwater Kent Manufacturing Ccmpany,l?hiiadelphia, Pa, a corporation of Pennsylvania Application October 23 1928, serial No. 314,512

, Renewed October '7, 1933 12 Claims. (c1. 179-471) Our invention relates to tuned amplifiers particularly as utilized in radio receiving apparatus to select and amplify currents of radio frequency.

In accordance with our invention, in an amplifier, particularly a multi-stage, radio-frequency amplifier, comprising cascaded tuned circuits and interposed vacuum tubes and in which capacities, and particularly inherent or natural capacities, are utilized in 'a relation effecting or contributing to stability of the amplifier, the voltage transformation ratios of transformers, preferably disposed in output systems of the tubes, are varied as the circuits are tuned to different frequencies to maintain substantially constant the stability of the system and the stabilising effect of the capacities.

Further in accordance with our invention, and more specifically, a winding, particularly the primary, of one or more of the transformers comprises a section movable with respect to the remainder thereof and tothe secondary winding; preferably the'movable coil sections are movable in unison with the tuning elements, for example, condensers in shunt to the respective transformer secondaries. i

Still further in accordance with our invention, the stabilizing capacities are comprised,'at least in part, by capacities between stator elements of the tuning condensers, which inherent capacities vary with change in position of interposed rotor structure, and the change'in magnitude of the effective stabilizing capacities is compensated for by the change in the transformation ratio of the transformers.

Further and more specifically, in each of the transformers abov edescribed the maximum mutual inductance'between the movable or rotatable primary'winding section and thesecondary winding is less than the mutual inductance between the fixed primary section and the secondary winding to maintain a desired relative poling of the transformer primary and secondary windings for all positions of the movable primary section.

Our invention resides in the method, system,

and features of construction and arrangement hereinafter described and claimed. 7

For an understanding of our invention, reference is to be had to the accompanying drawings in which:

Fig. 1 is a diagrammatic circuit arrangement of radio receiving apparatus utilizing our invention. Fig. 2 is a fragmentary plan view of apparatus of Fig. 1.

Fig. 3 is a rear, in Figs. 1 and 2.

levational view of parts shown I spect to heater h to reduce hum.

Figs. 4 and 5 are plan and elevational views respectively, in section of transformer structure.

Fig. 6 is a perspective view of disassociated, component parts of the transformer of Figs. 4 and 5.

Referring to Fig. 1, the radiant energy absorbing structure comprises an antenna D, or equivalent, and the counter-capacity or earth E, connected respectively to an end of resistance R and a contact S slidable along the resistance to vary the amplitude of reproduced signals, generally as described and claimed in co-pending Miller application Serial No. 253,116, filed February 9,

1928. The resistance R is connected in shunt to the primary of an auto-transformer, preferably having a step-up ratio and comprising the untunable input circuit of a coupling tube V as described and claimed in co-pending Miller application Serial No. 263,272, filed March 21,1923. Thegrid g of the couplingtube is connected to one end of coil T and the radio-frequency. path to the other effective end of the auto-transformer secondary includes the condensers c, 0 having low impedance tocurrents of radio frequency connected' between conductors supplying current to the filament f of the coupling tube, and ground E,

or equivalent.- i

Inductively related to the primary P1 of transformer T1 in the anode circuit of tube V, is the secondary S1, in shunt'with which is connected the tuning condenser K1 for. effecting tuning of the input circuit of the amplifier tube VI inwhose anode circuit are included the fixed coil P2. and the movable coil p2, serially connected-and together formingthe primary of transformer T2 whose secondary S2 tuned by variable condenser 7 K2 is comprised in the input circuit of amplifier tube V2. V

The fixed and movable coils, .P3 and p3, respectively, are serially. connected in the anode circuit of tube V2 and constitute the primary of transformer T3 whose secondary S3 shunted by tun-. ing condenser K3 comprises the input circuit of tube V8 which may be utilized to demodulate amplified, radio-frequency current in which case,v there is provided the grid-condenser c1 and gridleak resistance R1. As the detector or demodulator tube V3 shown is of the alternating-current type having a heater in and a uni-potential cathode f,;the terminals of grid-leak r are connected to grid g and uni-potential cathode f of the tube. Resistance R6 of 6,000 ohms, for example, shunted by radio-frequency by-pass condenser C6, renders the uni-potential cathode 1 positive with re-1 In the anode circuit of the detector tube between the points e and 7' may be connected a telephone instrument, or as shown, the primary P4 of an audio-frequency transformer T4 whose secondary is connected in or to the input circuit of an amplifier of one or more stages.

Referring to Figs. 2 and 3, the tuning condensers which as shown are of the type described and claimed in U. S. Letters Patent 1,668,320 to Kent are mounted on metal supporting bracket 1 having a vertical panel 2 and a horizontal ledge 3 to which is attached an extension plate 4 of suitable insulation, as bakelite or other phenol condensation product, carrying mounting brackets 4 for the radio-frequency transformers T1, T2, etc. and

adapted to support tubes V, V1, V2 etc. as claimed in Kent "[1. S. Letters Patent 1,655,372. Preferably, the rotors of the tuning condensers, which are at ground, or low, potential are mechanically connected by belts 5 passing over drums 6 se-' cured ,to the shafts thereof to effect their movement in unison by structure similar to that claimed in Kent U. S. Letters Patent 1,668,155. Single dial operation is made possible by the interposition of coupling tube V between the antenna and the first tunable circuit as claimed in Miller Patent 1,639,414 granted August 16, 1927.

Between the elements of the input circuits for example, tuning condenser stators, of tubes V1 and V2 and between like circuits of tubes V2 and V3, there exists capacities, particularly natural or inherent capacities k4, k5 which are effective when the transformer windings are relatively reversed, either by the manner of winding, or mode of connection, to effect stability of the tuned, radio-frequency amplifier stages and to suppress completely if desired, regenerative feed-back camed by couplings between the circuits, as for change in frequency and additionally in apparaw tus utilizinginherent capacities, the magnitude of the capacities changed due to change in position of the tuning elements. Referring to Figs. 2 and 3, it is apparent that as the position of the grounded rotor of condenser K2 interposed between the stators of. condensers K2 and K3 is changed, the effective, natural capacity between is changed To maintain substantially constant the relation between feed-back and counter feed-back effect, and if desired, to maintain substantially complete neutralization, for all frequencies to which the circuits are tunable, the transformation ratios of transformers T2 and T3 are varied as the circuits are tuned to different frequencies and preferably simultaneously therewith. In the arrangement. shown couplings 7 secured to the rotor shafts of condenser K2 and K3 engage the bent ends of shafts 8 of the movable primary coils p2 and p3 of transformers T2 and T3 to effect movement in unison of the condenser rotors and coils p2 and p3.

The number of turns or inductance of the fixed coils P2 and P3 which as shown in Figs. 2 l and 3 may be wound over respective secondaries the radio-frequency potentials of the anodes of tubes V1 and V2 are always opposite in polarity to the potentials of the grid terminals of the associated secondaries.

The secondaries S1, S2, and S3 in radio apparatus capable of receiving signals having wave lengths within the broadcast range, may each comprise about 112 turns of #36 B 8; S gauge wire on a tubular form 9 of suitable insulating material, as bakelite, fibre, or the like, having a diameter of about 1%". The primary winding P1 of about 13 turns of #36 B it S gauge wire is Wound directly over secondary S1, preferably at the cathodeend thereof, suitable insulation as a strip of varnished cambric, or the like, being interposed between the windings, if desirable or necessary. The fixed primary coils P2 and P3 of transformers T2 and T3 each similarly wound over the associated secondary, are of about 8 turns of"#36 B & S gauge Wire. Within the forms 9 of transformers T2 and T3 are disposed the rotatable supports 16 of the movable primary coils p2 and p3 in position effecting their inductive re:

terial is placed within tube 9 with the ears or lugs 13 projecting through holes in the tube which when bent against the outside thereof secure the bearing strip 12 in position to receive shaft 14 of the coil rotor 10. Thereafter the assembled rotor including form 10, and shafts 14 and 15 to which are soldered the ends of the coil wound thereon is passed through slot 16 of the secondary form 9, the shoulder 17 on shaft 14 engaging the rear bearing plate 12, The curved, front bearing plate 18 of phosphor bronze, or the like, receiving shaft 15 of the coil rotor is sprung into the position most clearly shown in Fig. 4, with lugs 19 thereof projecting into or through holes 20 of the tubular, secondary form 9. The rear face of plate 16 presses against shoulder 21 of shaft 15 to prevent rectilinear movement of the rotor. Conductors are soldered to the bearing plates 12 and 18 to effect electrical connection with the terminals of the coil wound in groove 11.

The coil and condenser rotors of each stage are mechanically connected and the electrical relaposition effecting tuning of the amplifier input circuits to the highest wave length or lowest frequency to which they are capable of responding, the fixed and movable coils are in maximum assisting relation, that is the magnetic fields produced by current flowing through them are cumulative in their effect upon the secondary associated therewith. When the tuning condensers are at their minimum setting to tune the amplifier circuits to the highest frequency to which they are capable of being tuned, the fields produced by the fixed and movable coils are in maximum opposition so that only their diiference is effective upon the secondary inductively related thereto. As the amplifier circuits are tuned to high and higher frequencies, the voltage-transformation ratio of the radio-frequency transformers is therefore simultaneously increased, maintaining the counter feed-back effects substantially equal and opposite to feed-back effects for-all wave lengths within the range to which the circuits are tunable.

be utilized to supply current Hithertofore, in tunedradio-frequency amplifiers utilizing transformers having fixed coupling, increase of resistance or resistance effects have been utilized to compensate for the increasing. tendency to instability of the amplifier at the lower wave-lengths with adverse effect upon the selectivity of the amplifier. In the arrangement described by selection of proper values of the fixed and movable coils, for examplaas abovede scribed, it-is not necessary to use resistances or their equivalent, which simplifies the apparatus by eliminating these damping elements and improves selectivity. Further, the selectivity is maintained at a high value as the circuits are tuned to the higher frequencies since the voltage ratio of the secondary to the primary of the transformers is increased by the tuning operation.

The change in magnitude of the inherent ca pacities 704 and k5 which occurs as the position of the tuning condenser rotors is varied, is at all times in a sense which is opposite to the sense of change in the voltage-transformation ratio of the transformers T2 and T3 to effect stability of the amplifier at all frequencies within its tuning range. 7

Referring again to Fig. l, the tubes V, V1 and V2 of a type having a filament adapted to be'heated from an alternating current source, are supplied from the secondary 22 of a transformer whose primary 23 is connected through regulating resistance 24 and switch 25 to a source of alternating current source 26. For convenience,

a plug and socket connection not shown may be utilized to connect the transformer primary to house wiring or equivalent standard power circuit.

The heater h of tube V3 is supplied froin'transformer secondary 2'? with current from which is" derived heat to render the equi-potential cathode secondaries 22 and 28 may to other tubes not shown, for example tubes'employed in audio-frequency amplifier stages.

The terminals of secondary 29 are connected to the anodes of a full wave rectifier 30 of the thermionic type having a cathode J heated by current from transformer secondary 31. Conductor 32 from the cathode of the rectifier tube 30 to the anodes of thermionic tubes V, V1, V2, ,etc. includes the inductances L which together with condensers C2, comprise a filter system for suppressing ripples of the rectified anode current. Conductor 33 from a mid-tap of secondary 29 to a mid-tap of resistance R2 connected across filament secondary 22, includes a resistance R3 electron-emissive.

'whose low potential end is connected to earth E or equivalent. The fiow of anode current tial which is utilized to maintain the grids g of tubes V, V1 and V2 negative with respect to their associated cathodes. To prevent reaction between tube circuits, particularly modulation of the radio-frequency signal energy, there is included in that portion of conductor 32- connected to the anode circuits of the detector and audio-amplifier tubes, a suitably high resistance R4 between the anode end of which and ground is connected condenser C3.

What we claim is:

1. In tuned amplifiers utilizing one or'more transformers, the method of stabilization which comprises utilizing inherent capacity and reversal of transformer windings to effect stability, and varying the voltage transformation ratio of a transformer as the amplifier is tuned to different frequencies to compensate forvariation in effectiveness of stabilizing capacity.

2. In tuned amplifiers utilizing one or more transformers, the method of stabilization-which comprises utilizing inherent capacities and reversal of transformer windings to effect stability, and varying the voltage transformation ratio of the transformers in the same sense that the resonance frequency is changed as the amplifier is tuned from one frequency to another frequency, and to an extent maintaining substantially constant-the stabilizing effect of the capacities. i

3. In tuned amplifiers comprising one or more transformers and tuning devices, the method which comprisesutilizing inherent capacities between fixed elements of the tuning devices as stabilizing capacities, adjusting movable elements of the tuning devices to adjust the amplifier to resonance from one frequency to another frequency, which adjustment affects the magni tudes of the stabilizing capacities, and varying the voltage transformation ratios of the transformers to compensate for the changes in magnitude of the stabilizing capacities.

4. In tuned amplifiers comprising one or mor transformers and tuning devices, the method which comprises utilizing inherent capacities between fixed elements of the tuning devices as stabilizing capacities, adjusting movable elements of the tuning devices to adjust the amplifier to resonance from one frequency to a higher frequency, which adjustment decreases the magnitudes of the stabilizing capacities, andsimultaneously therewith, increasingthe voltage transformation ratio of the transformers to compensate for the decrease in magnitude of the stabilizing capacities.

5. In an amplifier of one or more: stages comprising cascaded tuned circuits'including trans former secondaries tuned by devices having movable -.elements, the method -which comprises utilizing inherent capacities between elements of the circuits in a stabilizing relation, adjusting the movable elements of the tuning devices to tune the circuits from resonance at one frequency to resonance at a higher frequency, which adjustment decreases the magnitude of the natural stabilizing capacities, and increasing the voltage transformation ratios of the transformers to maintain substantially constant the stabilizing effect of the capacities.

6. A stabilized amplifier comprising a thermionic tube, transformers in the input and outi put systems thereof having reversed windings, tuning condensers in shunt to the secondaries of said transformers arranged so that the capacity between the condenser stators cooperates with the reversed windings to effect stability, and means to vary the transformation ratio of the transformer in the output system to comled effect movement of said movable section to vary the transformation ratio of the transformer in a sense compensating for the changes in magnitudes of said natural capacities effected by movement of the adjustable elements of said tuning devices.

8. A multi-stage amplifier comprising thermionic tubes, input and output systems therefor tunable by condensers having adjustable el ments, transformers having their primary windings in the anode circuits of said tubes and their relatively reversed secondary windings co--operating with capacities between said systems to effect stability, said capacities decreasing in magnitude as said adjustable condenser elements are varied to tune to higher frequencies and means movable simultaneously with said adjustable elements to increase the voltage transformation ratio of said transformers said elements are tuned to higher frequencies.

9. The combination with an amplifier tube, of a capacity area connected to the control electrode thereof, a transformer whose primary is in the output circuit of'said tube, a condenser for tuning the secondary circuit of said transformer and constituting a capacity area formi g a stabilizing capacity with said first named capacity area, said stabilizing capacity decreasing in magnitude as said condenser is adjusted to tune to higher frequencies and means for increasing the ratio of voltage transformation of said transformer as said condenser is adjusted to tune to higher frequencies to compensate for the decrease in magnitude of said stabilizing capacity.

10. Stabilized radio-receiving apparatus comprising thermionic tubes, tuning condensers in the input circuits thereof having stator androtor structures With inherent capacity between the stator structures whichis reduced as the rotor structures are moved to tune said circuits higher frequency, a transformer for coupling said tubes having relativelyreversed windings to effect counter feed-back through said inherent capacity, and means for increasing the voltage-transformation ratio of said transformer as said condensers are adjusted to tune said circuits to higher frequency to compensate for said decrease in inherent capacity.

11. Stabilized radio-receiving apparatus comprising a thermionic tube, condensers for tuning the input and output systems of said tube, said condensers being so positioned that inherent capacity exists between them, said condensers being of such structure and so disposed that said inherent capacity is reduced as the adjustable elements of said condensers are moved to tune said systems to higher frequency, a transformer in the output system of said tube having relatively reversed windings to effect counter feedback through said inherent capacity, movable means for increasing the voltage-transformation ratio of said transformer as the adjustable elements of said condensers are moved to tune said systems to higher frequency to compensate for said decrease in inherent capacity, and means for coupling said movable means and the adjustable elements of said condensers to effect their actuation in unison.

l2. Stabilized radio-receiving apparatus comprising'therniionic tubes, tuning condensers having their stators connected to the control electrodes of respective tubes and so disposed that inherent capacities between the stators are reduced as the'condenser rotors are adjusted to tune the'input circuits of said tubes for higher and higher frequencies, coupling transformers having reversely poled windings to effect counter feed-back throughsaid inherent capacities, and means operable in unison with said condenser rotors to change the coupling of the windings of said transformers while maintaining reversed paling thereof to increase, the voltage transformation for higher and higher frequencies, and thereby to compensate for said decrease in magnitude of said inherent capacities.

Joan M. MILLER. SARKES TARZIAN. 

